The respiratory center

So in this video what
I wanted to focus on is one particular area of the
brain-- actually, two areas I'm going to sketch
out, not just one. I'm going to show you how I
think that these two areas can be kind of united in a way. So, these two areas,
where I'm sketching out these little green
circles, are going to be responsible for
breathing-- how fast you breathe, how deep you breathe. And there are lots of little
neurons in these two areas. And these neurons are
going to be communicating. Let's say this neuron sends
a little axon on down here, maybe this guy sends
an axon up here. They're going to be
communicating information among themselves and
between themselves to kind of make sure they're
working in a coordinated way so that the
breathing that you do is the way that it
should be, you know, how fast it should be, given
a particular situation. So the way I think of it is
kind of uniting these two areas. In fact, sometimes it's
subdivided even further. I just put it all together
and say this part of the brain that I'm just
sketching out in green, this area then, is our
respiratory center. This is going to be
responsible for all of the important
activities of breathing. So let me just
write that out here. Respiratory center. So our respiratory
center is going to gather information
from different places. And then it's going to
have to make a decision and execute based on all
the information it receives. So one key piece
of information is going to come from cells right
here, neighborhood cells. And these cells are called
the central chemoreceptors. The reason I'm
calling them central is because they're also
part of the brain, right? They're right in the
same neighborhood, and so these central
chemoreceptors don't have to go too far to
communicate their information. And specifically they're
going to gather information on things like carbon
dioxide levels and pH levels. One thing they don't
do is oxygen levels. So that's these guys right here. So if you have
central chemoreceptors you also probably
can expect that there would be some peripheral
chemoreceptors, and these ones are
also very important. And they exist
outside of the brain, so they're going to be actually
sending their information along through neurons
that are going to extend all the
way into the brain. So for example, you might
have two key groups. One is called the aortic
body and the other is called the carotid body. Aortic body and
the carotid body. They're coming from
different locations and are actually going
to use different nerves to get into the brain. So the carotid
body, for example, is going to extend out
this way through a neuron. And that's going to be through a
nerve called the-- right here-- called the
glossopharyngeal nerve. This is cranial nerve
number nine, also called the
glossopharyngeal nerve. So this is one of the key
peripheral chemoreceptors. You've also got some nerves
or neurons projecting from the aortic body going
through the vagus nerve. So this is our vagus nerve,
or cranial nerve number 10. It goes by two different names. These peripheral
chemoreceptors are going to detect
things like oxygen-- in fact, that's probably one of
the most important things they detect-- as well as
carbon dioxide and pH. So that's information coming
to the respiratory center from our peripheral and
central chemoreceptors then is mostly about chemicals. In addition, there's
another whole group of receptors called
mechanoreceptors. And these ones
are actually going to be sending information
about pressure. Now you may be thinking,
well, wait a second. I thought baroreceptors
told us about pressure. And it turns out, baroreceptors
are one type of mechanoreceptor that's found inside
of the blood vessels. So there are many other types
and many other locations. And so the bigger, more general
term would be mechanoreceptor. You can find them in
places like the nose, you can find them in the
lungs, in the GI tract, so lots of different locations
for these mechanoreceptors. And they're all sending
their own projection over to the respirator center. And in fact, the
lungs and the GI tract are going to hitch a
ride in this vagus nerve and the nose
mechanoreceptors they're going to travel through
another nerve that's called the trigeminal nerve
or cranial nerve number five. So these are the routes
that these receptors are going to take to get
to that respiratory center. But how do these work exactly,
these mechanoreceptors? Let's take an example. Let's say you're walking
and you inhale some pollen. Well, that's going to trigger
one of these mechanoreceptors in your nose and
it's going to want to relay that information over
to your respiratory center so you're going to
get a little nerve impulse through that
cranial nerve number five. Similarly in your
lungs, let's say you actually inhale
some cigarette smoke. And let's say the
lungs don't like that. And then the mechanoreceptor
feels that little particle. It's going to
trigger cranial nerve number 10, the vagus nerve. Similarly, you have
these stretch receptors that are in the lungs. And these are actually
kind of interesting because what they're
doing is they're saying, hey, you know these lungs are
starting to get really, really full, really
distended, and so they want to let the respiratory
center know that maybe it's time to exhale. And similarly, in the GI
tract you can imagine, let's say a baby is taking
milk and the stomach is getting really
distended, you might also imagine that that
information would go back to the respiratory center
as well, in this case through cranial nerve number 10. So we have information
about pressure or stretch, we also have information
about chemicals coming in. But what about information
on things like, I don't know, things like
anxiety for instance, or fear. Let's say someone is
having these emotions. Their breathing
pattern may change. Maybe they're in pain. So these kinds of
things are actually coming from the hypothalamus. So this is another region
of the brain that's sending information down
to the respiratory center and helping to affect
how we breathe. And finally, this is
probably the largest part of our picture, this
is our cerebrum. And the cerebrum is responsible
for all the voluntary stuff that we do, things
like singing, where you've got to
control your breath. Or maybe you're playing
a musical instrument, or maybe you're
yelling or screaming. Let's put yelling down here. Anything like that, you're going
to want to control your breath. And so that's all
voluntary control. So this is our
voluntary control. And it's good that actually
we have this mechanism so we can-- if we want to--
we can change our breathing pattern. But it's also great that
our respiratory center can work on its own. Can you imagine if you
had to always think about taking a breath? You couldn't do
anything else, right? You couldn't sleep,
you couldn't eat. You would always
just be thinking about taking a breath
so that you wouldn't miss the next breath and
subsequently run out of air. So this is all the
information coming into our respiratory center. Let me just scoot this over
and actually show you now what our brain can do with that
information to actually make sure that we're
breathing comfortably. This is our spinal column. And I'm actually just
going to label out the motor nerves and some
of the muscle groups. So we've got motor
nerves and muscle groups. And there are four
key muscle groups that are going to be controlled
by our respiratory center. And we're going to go
through them one by one. So the first one, and the one
that people usually always talk about or think about,
is this one right here. This is going to
be C3, C4, and C5. So C3 through C5, and the
muscle is the diaphragm. This is the giant muscle
that kind of sits right below our lungs and
when it contracts you take in a nice deep breath. But it doesn't work alone. We've got other muscles
involved as well. So I'm actually
going to sketch out what these other
muscle groups are. The first one is T1 through T11. All these levels are going
to send off a little nerve. And each nerve will go through
a different intercostal muscle. So intercostal
muscles are-- these are the muscles that kind
of go between the ribs-- these are going to help expand
or pull out your ribs, right? So these are important
for breathing as well. A little bit lower
then, you also have these abdominal muscles. Abdominal muscles here are
going to be T6 through L1. These are the levels
where the little nerve fibers come out and are going
to help innervate or help these muscles, abdominal
muscles, contract. So this is a third
group of muscles and they're controlled
by these spinal levels. And the final group would
be this group up here. So this is actually
C1 through C3. And these would be
the accessory muscles. Accessory muscles are
the ones-- usually I think of them as the
ones around your neck area. And they're going to also kind
of help pull out the rib cage and expand the lungs. So there you have it. You have information
coming in, that's the stuff that we
started talking about, from all the
different locations, around chemicals,
information about pressure, and your emotional
status, and what you're thinking about
doing involuntarily. All that information
is going to come in and then the
respiratory center has to decide how to kind of
balance all that information. And on the way out
it's going to be able to execute by controlling
all these different muscle groups and sending information
down the motor nerves that we just listed to these
four big groups of muscles.